LandscapeGeometry.ts

import { BufferAttribute, BufferGeometry } from 'three'

export const outerWidth = 200
export const outerLength = 200

export default class LandscapeGeometry extends BufferGeometry {
  private innerWidth: number
  private innerLength: number

  constructor (inWidth = 200, inLength = 100) {
    super()
    this.innerWidth = Math.min(inWidth, outerWidth - 2)
    this.innerLength = Math.min(inLength, outerLength - 2)
    this.setAttribute('position', new BufferAttribute(this.vertices, 3))
    this.setAttribute('uv', new BufferAttribute(this.uvs, 2))
    this.setIndex(new BufferAttribute(this.indices, 1))
    this.computeVertexNormals()
  }

  get vertices (): Float32Array {
    const ox = Math.abs(outerWidth) / 2
    const oz = Math.abs(outerLength) / 2
    const dx = Math.abs(this.innerWidth) / 2
    const dz = Math.abs(this.innerLength) / 2

    return new Float32Array([
      // North
      -ox, 0, -oz, -dx, 0, -dz, +ox, 0, -oz,
      +dx, 0, -dz, ox, 0, -oz, -dx, 0, -dz,

      // East
      +ox, 0, oz, +ox, 0, -oz, +dx, 0, -dz,
      +ox, 0, oz, +dx, 0, -dz, +dx, 0, +dz,

      // South
      +ox, 0, +oz, +dx, 0, +dz, -ox, 0, +oz,
      -ox, 0, +oz, +dx, 0, +dz, -dx, 0, +dz,

      // West
      -ox, 0, +oz, -dx, 0, +dz, -ox, 0, -oz,
      -ox, 0, -oz, -dx, 0, +dz, -dx, 0, -dz
    ])
  }

  get uvs (): Float32Array {
    const du = (outerWidth - this.innerWidth) / 2 / outerWidth
    const dv = (outerLength - this.innerLength) / 2 / outerLength

    return new Float32Array([
      // North
      0, 1, du, 1 - dv, 1, 1,
      1 - du, 1 - dv, 1, 1, du, 1 - dv,

      // East
      1, 0, 1, 1, 1 - du, 1 - dv,
      1, 0, 1 - du, 1 - dv, 1 - du, dv,

      // South
      1, 0, 1 - du, dv, 0, 0,
      0, 0, 1 - du, dv, du, dv,

      // West
      0, 0, du, dv, 0, 1,
      0, 1, du, dv, du, 1 - dv
    ])
  }

  get indices (): Uint32Array {
    return new Uint32Array([
      0, 1, 2,
      3, 4, 5,
      6, 7, 8,
      9, 10, 11,
      12, 13, 14,
      15, 16, 17,
      18, 19, 20,
      21, 22, 23
    ])
  }
}